<script type="text/javascript">
  // rem单位基准声明
  var designWidth = 375, maxWidth = 500, bodyFontSize = 16, baseFontSize = 100
  _setBaseFontSize()
  _setBodyFontSize()
  _setReCalcRem()

  // 设置文档默认字体
  function _setBodyFontSize () {
    if (document.body) document.body.style.fontSize = bodyFontSize + 'px'
    else document.addEventListener('DOMContentLoaded', _setBodyFontSize, false)
  }

  // 设置REM基准字号 1rem = 设计图尺寸 / 屏幕dpr / 基准字号
  function _setBaseFontSize () {
    var clientWidth = document.documentElement.clientWidth
    var rem = baseFontSize * Math.min(clientWidth, maxWidth) / designWidth
    document.documentElement.style.fontSize = rem + 'px'
    window.rem = rem / 100
  }

  // 设置屏幕尺寸变化事件代理, 重新计算REM基准尺寸
  function _setReCalcRem () {
    document.addEventListener('DOMContentLoaded', _setBaseFontSize, false)
    window.addEventListener('orientationchange' in window ? 'orientationchange' : 'resize', _setBaseFontSize, false)
  }
</script>